1. Technical Field
The present invention relates to a discharge lamp having a discharge container made of quartz glass, and a light source device and a projector using the same.
2. Related Art
For a light source device used in a projector, for example, a discharge lamp such as an ultra-high pressure mercury lamp is mainly used. For a discharge container forming the discharge lamp, high-purity quartz glass is often used. The high-purity quartz glass has high viscosity and unyielding properties. Further, the high-purity quartz glass is hard to be crystallized even at a high temperature and may secure sufficient light transmissivity in a certain period as the discharge container.
However, there has been a problem that, even in the case of using quartz glass, for use in a long time and a long period, it is finally crystallized (devitrified). Further, there has been another problem that, with the use in a long time and a long period, an electrode made of tungsten becomes thinner.
In order to solve the problems, an attempt to suppress crystallization of silica glass has been made by forming a boron oxide film on an inner surface of the discharge container (Patent Document 1 (JP-A-2010-198977)). However, according to this method, crystallization of the quartz glass may be suppressed to some degree, but, for example, the thinning of the tungsten electrode may not necessarily be suppressed. Further, containers using a thin film of cubic boron nitride (c-BN), a thin film of silicon boron nitride (SiBN), a protective film of yttrium oxide, or the like have been known (Patent Document 2 (JP-A-6-333535), Patent Document 3 (JP-A-9-147801), and Patent Document 4 (JP-A-2008-270074)), however, in the cases, chemical vapor deposition (CVD) has been used for all of them, and it has been difficult to form them thicker on the inner surfaces of the discharge containers.